U.S. patent application number 14/376492 was filed with the patent office on 2015-01-15 for method for recovering lithium.
This patent application is currently assigned to SUMITOMO METAL MINING CO., LTD.. The applicant listed for this patent is Satoshi Asano, Hitoshi Ishida, Takayuki Nakai. Invention is credited to Satoshi Asano, Hitoshi Ishida, Takayuki Nakai.
Application Number | 20150013499 14/376492 |
Document ID | / |
Family ID | 48947101 |
Filed Date | 2015-01-15 |
United States Patent
Application |
20150013499 |
Kind Code |
A1 |
Asano; Satoshi ; et
al. |
January 15, 2015 |
METHOD FOR RECOVERING LITHIUM
Abstract
To provide a method for recovering lithium, that is capable of
efficiently recovering lithium without containing impurities, such
as phosphorus and fluorine, from a lithium-containing solution
containing lithium hexafluorophosphate and separated from a lithium
ion battery. In the present invention, alkali hydroxide is added to
the lithium-containing solution and the solution is made to have pH
9 or more, a precipitate of a phosphate and a fluoride salt is
formed, the formed precipitate is separated and removed, and then
lithium is recovered from filtrate.
Inventors: |
Asano; Satoshi; (Ehime,
JP) ; Ishida; Hitoshi; (Ehime, JP) ; Nakai;
Takayuki; (Ehime, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Asano; Satoshi
Ishida; Hitoshi
Nakai; Takayuki |
Ehime
Ehime
Ehime |
|
JP
JP
JP |
|
|
Assignee: |
SUMITOMO METAL MINING CO.,
LTD.
Tokyo
JP
|
Family ID: |
48947101 |
Appl. No.: |
14/376492 |
Filed: |
February 10, 2012 |
PCT Filed: |
February 10, 2012 |
PCT NO: |
PCT/JP2012/053159 |
371 Date: |
August 4, 2014 |
Current U.S.
Class: |
75/739 |
Current CPC
Class: |
Y02E 60/10 20130101;
C22B 7/006 20130101; Y02P 10/20 20151101; C22B 26/12 20130101; C22B
3/0005 20130101; H01M 10/052 20130101; Y02W 30/84 20150501; H01M
10/54 20130101; C22B 3/44 20130101 |
Class at
Publication: |
75/739 |
International
Class: |
C22B 26/12 20060101
C22B026/12 |
Claims
1. A method for recovering lithium from a lithium-containing
solution containing lithium hexafluorophosphate separated from a
lithium ion battery, the method comprising: a precipitate formation
process of adding alkali hydroxide to the lithium-containing
solution to cause the lithium-containing solution to have pH 9 or
more, and forming a precipitate of a phosphate and a fluoride salt;
and a lithium recovery process of recovering lithium from filtrate
after separating and removing the precipitate formed in the
precipitate formation process.
2. The method for recovering lithium according to claim 1, wherein
the alkali hydroxide is potassium hydroxide.
3. The method for recovering lithium according to claim 1, wherein
the lithium recovery process includes an extraction process of
adding an alkali solution to the filtrate to adjust pH to 8 or more
to 13 or less, and allowing an acidic extractant to be in contact
with the filtrate to extract lithium ions, and a stripping process
of allowing the acidic extractant having extracted the lithium ions
in the extraction process to be in contact with an acid solution
having pH 3 or less to strip the lithium ions.
4. The method for recovering lithium according to claim 3, wherein
the lithium recovery process includes a scrubbing process of
scrubbing the acidic extractant having extracted the lithium ions
in the extraction process, and performs the stripping process after
scrubbing.
5. The method for recovering lithium according to claim 4, wherein
the lithium recovery process further includes a lithium carbonate
deposition process of adding a carbon dioxide gas or a
water-soluble carbonate to a stripping liquid containing the
lithium ions obtained in the stripping process, and depositing a
lithium carbonate.
6. The method for recovering lithium according to claim 1, wherein
the lithium recovery process adds an alkali carbonate solution to
the filtrate, and deposits a lithium carbonate to recover
lithium.
7. The method for recovering lithium according to claim 1, wherein
the precipitate formation process adds the alkali hydroxide to a
lithium-containing solution that has been cleaned with water in
advance.
Description
TECHNICAL FIELD
[0001] The present invention relates to a method for recovering
lithium from a lithium ion battery, and especially relates to a
method for recovering lithium, which is capable of preventing
contamination by phosphorus and fluorine and recovering lithium of
high purity from a lithium-containing solution that contains
lithium hexafluorophosphate.
BACKGROUND ART
[0002] Effective use of electric power is required for recent
global warming tendency. Secondary batteries for electric power
storage are expected as one means, and from the standpoint of
prevention of air pollution, early practical application of large
secondary batteries is expected as an automobile power source.
Further, a demand of small secondary batteries has been steadily
increasing especially in association with spread and performance
enhancement of electrical devices, such as digital cameras and
mobile phones, as back-up sources of computers and power sources of
small household electrical appliances.
[0003] As these secondary batteries, a secondary battery having
performance corresponding to a device to be used is required, and
typically, lithium ion batteries are mainly used.
[0004] In the lithium ion battery, a negative material formed such
that a negative active material of graphite, or the like is fixed
to a negative substrate made of a copper foil in a metal packaging
can of aluminum, iron, or the like, a positive electrode material
formed such that a positive electrode active material of lithium
nickel oxide, lithium cobalt oxide, or the like is fixed to a
positive electrode substrate made of an aluminum foil, a current
collector made of aluminum or copper, a separator made of a resin
film, such as a polypropylene porous film, an electrolyte solution,
an electrolyte, and the like are enclosed.
[0005] By the way, establishment of measures against environment
pollution with used lithium ion batteries is strongly required for
an expanding demand of lithium ion batteries, and recovery and
effective use of valuable metals have been examined.
[0006] As a method for recovering the valuable metals from a
lithium ion battery having the above structure, for example, dry
melting treatment and incineration treatment for discharging the
battery and decomposing and removing a solvent, as described in
Patent Literature 1, are often used. Patent Literature 1 discloses
pretreatment to roast a lithium ion battery at a temperature of
350.degree. C. or more, to perform pulverization, and then to
perform screening.
[0007] However, in the case of dry treatment like the technology
described in Patent Literature 1, consumption of energy and exhaust
gas treatment are problems. Further, especially, in a melting
method, lithium is made into slag and becomes unrecoverable, and in
a roasting method, contained phosphorus and fluorine are fixed as a
water-insoluble phosphate and fluoride. Lithium, cobalt, nickel, or
the like that are valuable metals are contaminated. As a result,
separation and refinement become difficult. Therefore, direct
regeneration of lithium, cobalt, and nickel recovered in dry
roasting treatment for battery materials is difficult in terms of
quality, and effective reuse cannot be achieved.
[0008] Meanwhile, methods of recovering the valuable metals by wet
treatment have been proposed. However, even in such methods using
wet treatment, dry treatment is partly used, and realization of low
cost is difficult because of complexity of a treatment process.
Therefore, the valuable metals cannot be efficiently recovered.
[0009] Especially, regarding lithium of a valuable metal, there is
a problem that impurities, such as phosphorus and fluorine, are
mixed in, and thus high-quality lithium cannot be efficiently
recovered in the form of a simple substance. To be specific, a
lithium ion battery contains, as an electrolyte, lithium
hexafluorophosphate (LiPF.sub.6) and the like that constitute
lithium that is a valuable metal. This lithium hexafluorophosphate
has a hydrolysis reaction through wet treatment, and forms a
precipitate in the forms of lithium phosphate (Li.sub.3PO.sub.4)
and lithium fluoride (LiF), and lithium cannot be efficiently
recovered in the form of a simple substance.
[0010] While hexafluorophosphate ions in an electrolyte solution do
not form slightly soluble salts with metal ions other than
potassium and aluminum, the hexafluorophosphate ions form the
slightly soluble salts with the majority of metal ions when
hydrolyzed and changed into phosphate ions and fluoride ions. When
separation and refinement treatment is performed in the coexistence
of these hydrolysates, ions of these hydrolysates are precipitated
on products, resulting in quality failure.
[0011] As a method for removing hexafluorophosphate ions, for
example, Patent Literature 2 describes a method for adding
potassium fluoride and ammonium fluoride, forming slightly soluble
hexafluorophosphate and lithium fluoride, and separating the
hexafluorophosphate and lithium fluoride as a precipitate. However,
the technology described in Patent Literature 2 has problems that
phosphorus, fluorine, and lithium are recovered as a
coprecipitation mixture, already hydrolyzed phosphate ions cannot
be separated, and excessively added fluoride is remained in mother
liquor.
[0012] Further, Patent Literature 3 discloses a method for
absorbing hexafluorophosphate ions with a basic ion exchange resin,
preferably a weak basic ion exchange resin. However, because
behavior of the already hydrolyzed phosphate ions and fluoride ions
is different, there is a limit to remove the phosphate ions and the
fluoride ions at the same time, and even the technology of Patent
Literature 3 cannot sufficiently remove the phosphate and the
fluoride.
[0013] Meanwhile, Patent Literature 4 discloses a method for
remaining hexafluorophosphate ions in an extraction residual liquid
by using a positive ion exchange-type acidic extractant, and
selectively extracting and separating only lithium ions. However,
even the technology described in Patent Literature 4 has problems
that, in a process of adjusting a solution to have necessary pH for
extraction, the hexafluorophosphate ions are hydrolyzed and a
precipitate of lithium phosphate and lithium fluoride is generated,
becomes crud, and is physically mixed in an extraction solvent, and
lithium is contaminated.
CITATION LIST
Patent Literature
[0014] Patent Literature 1: JP H06-346160 A [0015] Patent
Literature 2: JP 2000-030741 A [0016] Patent Literature 3: JP
2007-207630 A [0017] Patent Literature 4: JP 2007-122885 A
SUMMARY OF INVENTION
Technical Problem
[0018] Therefore, the present invention has been proposed in view
of the foregoing, and an objective is to provide a method for
recovering lithium, which is capable of recovering lithium without
contamination by phosphorus and fluorine from a lithium-containing
solution containing lithium hexafluorophosphate and separated from
a lithium ion battery.
Solution to Problem
[0019] As a result of diligent examination for achievement of the
above objective, the inventors have found out that they can recover
lithium without contamination by phosphorus and fluorine by adding
alkali hydroxide to a lithium-containing solution containing
lithium hexafluorophosphate and separated from a lithium ion
battery to raise pH, forming a precipitate of a phosphate and a
fluoride salt, and separating and removing the precipitate, and the
inventors have completed the present invention.
[0020] That is, the present invention includes, in a method for
recovering lithium from a lithium-containing solution containing
lithium hexafluorophosphate separated from a lithium ion battery, a
precipitate formation process of adding alkali hydroxide to the
lithium-containing solution to cause the solution to have pH 9 or
more, and forming a precipitate of a phosphate and a fluoride salt,
and a lithium recovery process of separating and removing the
precipitate formed in the precipitate formation process, and then
recovering lithium from filtrate.
Advantageous Effects of Invention
[0021] According to the present invention, by adding of alkali
hydroxide to the lithium-containing solution containing lithium
hexafluorophosphate to raise pH, the precipitate of a phosphate and
a fluoride salt can be efficiently separated and removed, and
lithium without contamination by phosphorus and fluorine can be
recovered from the filtrate.
BRIEF DESCRIPTION OF DRAWINGS
[0022] FIG. 1 is a diagram illustrating a process of recovering
lithium from a lithium-containing solution separated from a lithium
ion battery.
DESCRIPTION OF EMBODIMENTS
[0023] Hereinafter, a method for recovering lithium according to
the present invention will be described in detail in the following
order with reference to the drawing.
[0024] 1. An outline of the present invention
[0025] 2. A method for recovering valuable metals from a lithium
ion battery
[0026] 2-1. Recovery of nickel and cobalt
[0027] 2-2. Recovery of lithium
[0028] 3. Other embodiments
[0029] 4. Examples
1. An Outline of the Present Invention
[0030] The present invention is a method for recovering lithium
that is a valuable metal from a lithium ion battery, and is a
method for preventing contamination of mixing in of impurities of
phosphorus (P), fluorine (F), and the like, and efficiently
recovering lithium from a lithium-containing solution that contains
lithium hexafluorophosphate and is separated from the lithium ion
battery, to be more specific, from a lithium-containing solution,
such as process liquids including a discharge liquid and a cleaning
liquid discharged after slurry is filtered in a process of
recovering valuable metals from the lithium ion battery, or
filtrate of post-sulfidation process to generate nickel and cobalt
as sulfides.
[0031] In recovering valuable metals from a lithium ion battery,
treatment to discharge a used lithium ion battery by using a
discharge liquid, treatment to clean dismantled objects of the
battery by using a cleaning liquid, and the like are performed.
After the treatments, a solution of the discharged liquid and the
cleaning liquid discharged after slurry is filtered contains
lithium in the form of lithium hexafluorophosphate (LiPF.sub.6)
that is a component of an electrolyte that constitutes the lithium
ion battery. Further, the filtrate of post-sulfidation process to
precipitate a nickel/cobalt mixed sulfide from a leachate obtained
by leaching a positive electrode active material of the lithium ion
battery also contains lithium in the form of lithium
hexafluorophosphate, and the like. Therefore, it is desirable to
efficiently recover lithium from the lithium-containing solution,
such as the process liquids including the discharged liquid and the
cleaning liquid separated from the lithium ion battery, or the
filtrate of post-sulfidation process, and to use the recovered
high-quality lithium again as an electrolyte component in
manufacturing of a battery.
[0032] However, the lithium hexafluorophosphate dissolved in the
lithium-containing solution does not form a slightly soluble salt
with metal ions in a case of the form of hexafluorophosphate ions.
However, when the hexafluorophosphate ions are hydrolyzed and are
changed into phosphate ions and fluoride ions, the phosphate ions
and the fluoride ions form slightly soluble salts with the majority
of metal ion. Accordingly, these phosphate ions and fluoride ions
form a precipitate of a phosphate (Li.sub.3PO.sub.4) and a fluoride
(LiF) with lithium that is a valuable metal to be recovered.
Therefore, even if a water-soluble carbonate, or the like is added
to the lithium-containing solution to form a precipitate of a
lithium carbonate, and the separation and refinement treatment of
lithium is performed, the precipitate is in a state where
phosphorus and fluorine are coprecipitated, resulting in quality
failure, and separated lithium cannot be used as a component of a
positive electrode active material again.
[0033] Therefore, the present invention uses a characteristic that
the hexafluorophosphate ions in an electrolyte solution are stable
in the vicinity of neutrality but are hydrolyzed into phosphate
ions and fluoride ions in a strong acid region or in a strong
alkaline region in an electrolyte solution. First, the
hexafluorophosphate ions in the solution are hydrolyzed into the
phosphate ions and the fluoride ions by raising pH of the
lithium-containing solution. Because these phosphate ions and the
fluoride ions caused by hydrolysis form slightly soluble salts with
metal ions, the precipitate of the formed slightly soluble salts is
separated and removed, and lithium contained in the filtrate is
then recovered.
[0034] As described above, using the effect of partial precipitate,
the present invention decreases impurities by partially raising pH
before separating and recovering lithium as a lithium carbonate,
and the like, and forming and separating a lithium phosphate, a
lithium fluoride, or salts of coexisting impurities. According to
the present invention, the impurities of phosphorus and fluorine
are removed from the lithium-containing solution prior to
separation and recovery of lithium. Therefore, lithium of high
purity, in which phosphorus and fluorine are not mixed in, can be
effectively recovered.
[0035] Hereinafter, an embodiment (hereinafter, referred to as
"present embodiment") related to a method for recovering valuable
metals from a lithium ion battery, to which the present invention
is applied, will be further described in detail.
2. A Method for Recovering Valuable Metals from a Lithium Ion
Battery
[0036] First, a method for recovering valuable metals from a
lithium ion battery according to the present embodiment will be
herein described with reference to the process diagram illustrated
in FIG. 1. As illustrated in FIG. 1, the method for recovering
valuable metals includes a discharge process, a crush/crack
process, a cleaning process, a positive electrode active material
exfoliation process, a leaching process, and a sulfidation process.
Then, as a method for recovering lithium, a precipitate formation
process of using a lithium-containing solution, such as process
liquids including a discharge liquid and a cleaning liquid
discharged in the discharge process and the cleaning process and
separated from a lithium ion battery, or filtrate of
post-sulfidation process, adding an alkali to the
lithium-containing solution to raise pH, and forming precipitate of
a phosphate and a fluoride salt, and a lithium recovery process of
recovering lithium from filtrate from which the precipitate formed
in the precipitate formation process has been removed. Hereinafter,
a process of recovering nickel and cobalt from a lithium ion
battery, and a process of recovering lithium from a
lithium-containing solution, such as a discharge liquid and a
cleaning liquid discharged in the process of recovering nickel and
cobalt will be described in order.
<2-1. Recovery of Nickel and Cobalt>
(Discharge Process)
[0037] In the discharge process, when valuable metals are recovered
from a used lithium ion battery, the battery is discharged prior to
dismantlement of the used battery. Because it is dangerous if the
battery is in a charged state when dismantled by being crushed and
cracked in the crush/crack process described below, the battery is
discharged and is made harmless.
[0038] In the discharge process, a discharge liquid, such as a
sodium sulfate solution or a sodium chloride solution, is used, and
the used battery is discharged by being immersed in the solution.
Slurry is filtered from the discharge liquid after the discharge
treatment, and the discharge liquid is discharged. In the
discharged discharge liquid, components of an electrolyte and an
electrolyte solution that constitute the lithium ion battery are
liquated in association with the discharge treatment. That is, the
discharged liquid after the treatment, which contains lithium of
the electrolyte, the electrolyte solution, and the like, is
discharged.
(Crush/Crack Process)
[0039] In the crush/crack process, the used lithium ion battery
that has been discharged and made harmless is dismantled by being
crushed and cracked.
[0040] In the crush/crack process, the harmless battery is
dismantled into an appropriate size by using a normal crusher or
cracking machine. Further, the packaging can is cut off and the
internal positive electrode material and negative material can be
separated and dismantled. It is preferable to cut off separated
portions into a more appropriate size.
(Cleaning Process)
[0041] In the cleaning process, the electrolyte solution and the
electrolyte are removed by cleaning the dismantled objects of the
battery obtained through the crush/crack process with water or
alcohol. The lithium ion battery contains organic solvents, such as
ethylene carbonate, propylene carbonate, diethyl carbonate, and
dimethyl carbonate, and the electrolyte, such as lithium
hexafluorophosphate (LiPF.sub.6). Therefore, by removing of the
organic solvents and the electrolyte in advance, organic
components, phosphorus (P), and fluorine (F) are prevented from
being mixing in the leachate as impurities in the positive
electrode active material exfoliation process described below.
[0042] Water or alcohol is used for cleaning of the dismantled
objects of the battery, and the organic components and the
electrolyte are removed by being shaken or stirred. As the alcohol,
ethanol, methanol, isopropyl alcohol, or a mixed liquid thereof is
used. While carbonates are typically insoluble to water, ethylene
carbonate that is a component of the electrolyte solution is
arbitrarily dissolved in water, and other organic components have
some solubility to water. Therefore, carbonates can be cleaned by
water.
[0043] It is preferable to iteratively clean the dismantled objects
of the battery, and phosphorus, fluorine, and the like derived of
the organic components and the electrolyte are removed by the
cleaning process to an extent not to influence subsequent
processes.
[0044] In the cleaning process, the electrolyte solution and the
electrolyte contained in the battery are removed by cleaning with
water or alcohol. Therefore, slurry is filtered after the cleaning
treatment, and the cleaning liquid containing the electrolyte of
lithium hexafluorophosphate and an electrolyte solution of ethylene
carbonate and diethyl carbonate is discharged. That is, a cleaning
liquid after the treatment, which contains components containing
lithium of the electrolyte, the electrolyte solution, and the like,
is discharged.
(Positive Electrode Active Material Exfoliation Process)
[0045] In the positive electrode active material exfoliation
process, a positive electrode active material is exfoliated and
separated from a positive electrode substrate by immersing of the
dismantled objects of the battery obtained through the cleaning
process in an acid solution, such as a sulfuric acid aqueous
solution, an alkali solution, or a solution that contains
surfactant. In this process, the positive electrode active material
and an aluminum foil can be separated in a solid state by putting
and stirring of the dismantled objects of the battery in an acid
solution, such as a sulfuric acid aqueous solution, or a surfactant
solution. Note that, in this process, all of the dismantled objects
of the battery may be immersed in the sulfuric acid aqueous
solution or the surfactant solution. However, only a positive
electrode material portion may be selected from the dismantled
objects of the battery, and be immersed.
[0046] When a sulfuric acid aqueous solution, for example, is used
as the acid solution, pH of the solution is controlled to fall
within a range of pH 0 to 3. An input amount of the dismantled
objects of the battery to the sulfuric acid aqueous solution is 10
to 100 g/l. As the alkali solution, a sodium hydroxide solution, or
the like can be used, and its additive amount is 0.3 to 1.0 N.
Further, when the surfactant-containing solution is used, the type
of surfactant is not especially limited, and nonionic surfactant,
anionic surfactant, or the like can be used. An additive amount of
the surfactant is 1.5 to 10 weight %, and pH of the surfactant
solution preferably falls within a range of pH 5 to 9.
[0047] The dismantled objects of the battery having been subjected
to the positive electrode active material exfoliation process are
screened, and a positive electrode active material of lithium
nickel oxide, lithium cobalt oxide, and the like separated from the
positive electrode substrate, and things accompanying these are
recovered. When all of the dismantled objects of the battery are
processed, negative powder, such as graphite, which is a negative
material, and things accompanying the negative power are also
recovered. Meanwhile, portions of the positive electrode substrate
and the negative substrate, a portion of the packaging can made of
aluminum, iron, and the like, a portion of the separator made of a
resin film, such as a polypropylene porous film, a portion of the
current collector made of aluminum or copper (Cu), and the like are
separated and supplied to respective treatment processes.
[0048] In the positive electrode active material exfoliation
process, by exfoliating the positive electrode active material from
the dismantled objects of the battery by using the acid solution or
the surfactant-containing solution, solid portions, such as the
positive electrode active material and the aluminum foil, are
separated. Meanwhile, a process liquid other than the solid
portions, such as the acid solution, the alkali solution, or the
surfactant solution used in the exfoliation treatment, is
discharged as filtrate. In the filtrate, the electrolyte, the
electrolyte solution, and the like that have not been removed in
the cleaning process may be dissolved and contained.
[0049] Further, in the positive electrode active material
exfoliation process, when the positive electrode active material is
exfoliated by using the alkali solution, the used alkali solution
may be used as alkali hydroxide to be added in the precipitate
formation process described below in the lithium recovery.
Accordingly, the valuable metals can be efficiently recovered from
the lithium ion battery with low cost.
(Leaching Process)
[0050] In the leaching process, the positive electrode active
material exfoliated and recovered in the positive electrode active
material exfoliation process is leached in an acid solution and is
made into slurry, in the presence of a fixed carbon-containing
material, a metal having high reduction effect, or the like. By the
leaching process, the positive electrode active material is
dissolved in an acid solution, and nickel, cobalt, and the like
that are the valuable metals constituting the positive electrode
active material are made into metal ions.
[0051] As the acid solution used in dissolution of the positive
electrode active material, an organic acid can be used, in addition
to a mineral acid, such as sulfuric acid, nitric acid, or
hydrochloric acid. Further, the acid solution to be used has at
least pH 2 or less, and it is preferable to control pH to about 0.5
to 1.5 in consideration of reactivity.
(Sulfidation Process)
[0052] In the sulfidation process, the solution obtained through
the leaching process is introduced to a reaction container, and a
sulfidation agent is added, so that a sulfidation reaction is
caused, and nickel/cobalt mixture sulfide is generated. This allows
recovery of nickel and cobalt that are the valuable metals from the
lithium ion battery. As the sulfidation agent, a sodium sulfide, a
sodium hydrosulfide, or an alkali sulfide, such as a hydrogen
sulfide gas, can be used.
[0053] To be specific, in the sulfidation process, a nickel ion (or
a cobalt ion) contained in the solution obtained through the
leaching process become a sulfide by a sulfidation reaction with an
alkali sulfide according to a formula (1), (2) or (3).
Ni.sup.2++H.sub.2SNiS+2H.sup.+ (1)
Ni.sup.2++NaHSNiS+H.sup.++Na.sup.+ (2)
Ni.sup.2++Na.sub.2SNiS+2Na.sup.+ (3)
[0054] Addition of the sulfidation agent in the sulfidation process
is performed until a point of time when change of ORP in the
reaction solution does not happen by further addition of the
sulfidation agent. Note that, typically, the reaction is completed
within a range of -200 to 400 mV (a reference electrode:
silver/silver chloride electrode). Further, the solution used in
the sulfidation reaction has about pH 2 to 4. The temperature of
the sulfidation reaction is, but not especially limited to, 0 to
90.degree. C., preferably about 25.degree. C.
[0055] Note that in the formulae (1) and (2), an acid is generated
as the reaction proceeds, and the reaction is delayed. Therefore,
to facilitate and complete the reaction, it is preferable to add an
alkali, such as sodium hydroxide, in addition to the sulfidation
agent, to neutralize the generated acid.
[0056] By causing the sulfidation reaction in the sulfidation
process, nickel and cobalt that are the valuable metals contained
in the positive electrode active material of the lithium ion
battery can be recovered as a nickel/cobalt sulfide (sulfide
precipitate).
[0057] As described above, when nickel and cobalt are recovered
from the lithium ion battery, the solutions, such as the discharge
liquid used in the discharge treatment in the discharge process,
and the solution such as the cleaning liquid used for cleaning the
dismantled objects of the battery and cleaning the electrolyte and
the electrolyte solution in the cleaning process, are separated and
discharged from the lithium ion battery. Further, the filtrate
obtained through the sulfidation process to generate the
nickel/cobalt mixture sulfide is separated and discharged from the
lithium ion battery. These discharged solutions, such as the
discharge liquid and the cleaning liquid, and the discharged
filtrate of post-sulfidation process contain the electrolyte, such
as lithium hexafluorophosphate, which constitutes the lithium ion
battery. That is, the solutions and the filtrate are
lithium-containing solutions containing lithium
hexafluorophosphate. It is desirable to efficiently recover lithium
from the lithium-containing solutions without mixing in the
impurities of phosphorus and fluorine.
<2-2. Recovery of Lithium>
[0058] Therefore, in the present embodiment, a precipitate of
impurities of phosphorus and fluorine is formed by raising pH of a
solution, the solution being the lithium-containing solution
containing lithium hexafluorophosphate, such as the process liquids
including the discharged liquid and the cleaning liquid separated
from the lithium ion battery, or the filtrate of post-sulfidation
process. Then, after the formed precipitate is separated and
removed, treatment to recover lithium from the filtrate is
performed. This allows efficient removal of the impurities of
phosphorus and fluorine based on lithium hexafluorophosphate
contained in the discharge liquid and the cleaning liquid after the
treatment, and lithium can be recovered without being contaminated
by phosphorus and fluorine.
[0059] To be specific, the method for recovering lithium in the
present embodiment includes a precipitate formation process of
adding alkali hydroxide to the lithium-containing solution, such as
the process liquids including the discharge liquid and the cleaning
liquid containing lithium hexafluorophosphate separated from the
lithium ion battery, or the filtrate of post-sulfidation process,
to cause the solution to have pH 9 or more, and forming a
precipitate of a phosphate and a fluoride salt, and a lithium
recovery process of recovering lithium from the filtrate after
separating and removing the precipitate formed in the precipitate
formation process.
(Precipitate Formation Process)
[0060] In the precipitate formation process, a precipitate of a
phosphate and a fluoride salt is formed from the lithium-containing
solution containing lithium hexafluorophosphate, such as the
process liquids including the discharge liquid and the cleaning
liquid discharged in the process of recovering valuable metals from
a lithium ion battery, or the filtrate of post-sulfidation process
in which the nickel/cobalt mixture sulfide has been generated. In
the present embodiment, by adding of alkali hydroxide to the
solution, such as the discharge liquid and the cleaning liquid, and
adjusting pH to 9 or more, the precipitate of a phosphate and a
fluoride salt is formed.
[0061] As described above, while hexafluorophosphate ions in the
solution are stable in the vicinity of neutrality, the
hexafluorophosphate ions become hydrolyzed into phosphate ions and
fluoride ions in a strong acid region or in a strong alkaline
region. Therefore, by adding alkali hydroxide to the
lithium-containing solution, such as the process liquids including
the discharge liquid and the cleaning liquid, or the filtrate of
post-sulfidation process, to cause the solution to have pH 9 or
more, the hexafluorophosphate ions in the solution are hydrolyzed
into the phosphate ions and the fluoride ions (hydrolysis
treatment).
[0062] Then, the phosphate ions and the fluoride ions generated
through the hydrolysis treatment form slightly soluble salts with
the majority of metal ions. Therefore, the phosphate ions and the
fluoride ions form a phosphate (Li.sub.3PO.sub.4) and fluoride salt
(LiF) with lithium in the solution (precipitate formation
treatment). By causing the phosphate ions and the fluoride ions to
become slightly soluble salts, the precipitate of these slightly
soluble salts are separated and removed, whereby phosphorus and
fluorine can be efficiently removed from the solution.
[0063] Note that, as described below, when lithium is recovered by
a solvent extraction method in a subsequent process, the lithium
ions are extracted in an alkaline region when the solvent is
extracted. Therefore, it is preferable to decompose the solution in
an alkaline region rather than advancing the hydrolysis reaction in
an acid region.
[0064] The alkali hydroxide added to the lithium-containing
solution is not particularly limited. However, it is preferable to
use sodium hydroxide, potassium hydroxide, or the like, in terms of
economic performance. Especially, when a potassium hydroxide
solution is used, even if not all of hexafluorophosphate ions in
the solution are hydrolyzed and a part of the hexafluorophosphate
ions is remained, a precipitate of potassium hexafluorophosphate
(KPF.sub.6) can be formed and separated. Therefore, the potassium
hydroxide solution can be more preferably used. Further, when
potassium hydroxide is used, the potassium hydroxide can slightly
decreased the solubility of phosphorus and fluorine, compared with
other alkali hydroxides. Therefore, the potassium hydroxide
facilitates generation of a precipitate of phosphorus and fluorine,
and can separate and remove the precipitate. The alkali hydroxide
is added such that pH of the lithium-containing solution becomes 9
or more.
[0065] Note that, when exfoliation is performed by using the alkali
hydroxide solution in the positive electrode active material
exfoliation process in the process of recovering valuable metals,
the alkali hydroxide solution of post-treatment may be reused in
the precipitate formation treatment.
[0066] As the lithium-containing solution that is an object from
which lithium is to be recovered, as described above, the process
liquids, such as the discharged liquid and the cleaning liquid
extracted in the process of recovering valuable metals from a
lithium ion battery, or the filtrate of post-sulfidation process in
which the nickel/cobalt mixture sulfide has been generated can be
used. One type of these lithium-containing solutions may be used
alone, or a plurality of types of the lithium-containing solutions
may be used together.
[0067] To be specific, for example, the discharge liquid as the
lithium-containing solution is a discharge liquid used for
performing the discharge treatment when valuable metals are
recovered from a lithium ion battery, as described above, and is a
solution of sodium chloride, sodium sulfate, and the like. By
performing of the discharge treatment to a used lithium ion battery
by using the discharge liquid, lithium hexafluorophosphate that is
an electrolyte component is contained in the discharge liquid
discharged after the discharge treatment. That is, lithium is
contained in the discharged liquid after the treatment.
[0068] Further, for example, the cleaning liquid as the
lithium-containing solution is a cleaning liquid used for cleaning
the dismantled objects of the battery after the used lithium ion
battery is crushed and cracked, and is a solution of water,
alcohol, or the like. By cleaning the dismantled objects of the
battery by using the cleaning liquid, the electrolyte and the
electrolyte solution contained in the dismantled objects of the
battery are removed, and lithium hexafluorophosphate that is an
electrolyte component is contained in the cleaning liquid
discharged after the treatment. That is, lithium is contained in
the cleaning liquid after the treatment.
[0069] Further, for example, the filtrate of post-sulfidation
process as the lithium-containing solution is a filtrate obtained
by separating the precipitate of a sulfide in the sulfidation
process for generating nickel/cobalt mixture sulfide as described
above. In the filtrate, lithium hexafluorophosphate that is an
electrolyte component is contained, and that is, the filtrate is
the lithium-containing solution.
[0070] The lithium-containing solution that is the process liquids
including the discharge liquid and the cleaning liquid, or the
filtrate of post-sulfidation process may be used as it is after
recovery, and the hydrolysis treatment and the precipitate
formation treatment of the hexafluorophosphate ions by addition of
the alkali hydroxide may be performed. However, cleaning treatment
may be performed by using water prior to the pH adjustment by
addition of the alkali hydroxide. As described above, by cleaning
of the recovered lithium-containing solution by water first, and
adding of the alkali hydroxide to the cleaned solution, the
precipitate of a phosphate and a fluoride salt suspended in the
solution can be cleaned and removed. Accordingly, the recovered
lithium can be effectively prevented from being contaminated by
phosphorus and fluorine, and the precipitate can be prevented from
being an obstacle when lithium is recovered, whereby lithium can be
more efficiently recovered.
[0071] As described above, in the present embodiment, by adding of
the alkali hydroxide in the precipitate formation treatment, pH of
the lithium-containing solution is raised, the hexafluorophosphate
ions contained in the solution are hydrolyzed, and the phosphate
ions and the fluoride ions are formed. When the hydrolysis reaction
ends, these phosphate ions and fluoride ions form the precipitate
of lithium phosphate and lithium fluoride that are slightly soluble
salts with lithium contained in the solution, even if a special
additive agent is not used.
[0072] The precipitate formed in this way can be separated and
removed by performing of a filtration operation. Therefore, in the
precipitate formation treatment, phosphorus and fluorine that are
impurities can be effectively removed from the lithium-containing
solution, and lithium without mixing in of the impurities can be
effectively recovered from the filtered solution, from which
phosphorus and fluorine have been removed.
[0073] Note that, in this process, the total amount of lithium
coprecipitated with phosphorus and fluorine is a small amount of
the whole amount of lithium, and lithium can be separately
recovered from the formed precipitate.
(Lithium Recovery Process)
[0074] In the lithium recovery process, the precipitate of a
lithium phosphate and a lithium fluoride formed in the precipitate
formation treatment is separated and removed, and then lithium is
recovered from the filtrate. The method for recovering lithium from
the filtrate is not especially limited. However, examples include a
solvent extraction method and a carbonation method below.
[0075] A Solvent Extraction Method
[0076] As the method for recovering lithium from the filtrate, a
solvent extraction method can be used, for example. An example of
the solvent extraction method includes solvent extraction treatment
to extract and separate lithium by using an acidic extractant.
[0077] To be specific, the solvent extraction treatment by using an
acidic extractant, first, as an extraction process, adds an alkali
solution to the filtrate to adjust the pH to 8 or more to 13 or
less, and allowing the acidic extractant to be in contact with the
filtrate to extract lithium ions. Next, as a stripping process, the
solvent extraction treatment allows the acidic extractant that has
extracted lithium ions to be in contact with an acid solution
having pH 3 or less to strip the lithium ions.
[0078] As the acidic extractant used in the extraction process,
2-ethylhexyl phosphonic acid mono-2-ethylhexyl,
di(2-ethylhexyl)phosphoric acid, bis (2,4,4
trimethyl-pentyl)phosphonic acid, a mixture of phenyl alkyl
beta-diketone and trioctylphosphine oxide, or the like can be used,
for example. Among them, it is especially preferable to use a
phosphoric acid-based extractant, and for example, it is preferable
to use di(2-ethylhexyl)phosphoric acid.
[0079] As the alkali solution added in the extraction process, a
sodium hydroxide solution, a potassium hydroxide solution, a
calcium hydroxide solution, a magnesium hydroxide solution, or the
like can be used. By adding of these alkali solutions, pH of the
filtrate is adjusted to 8 or more to 13 or less. When pH is lower
than 8, an extraction rate of the lithium ions from the filtrate
with the acidic extractant becomes low, and when pH is higher than
13, dissolution of the acidic extractant used for solvent
extraction becomes remarkable. Therefore, by adjusting of pH to 8
or more to 13 or less, the lithium ions in the filtrate can be
efficiently extracted.
[0080] The acidic extractant used in the extraction process has a
characteristic to cause ion exchange with H, and to release the
extracted metal ions, by causing pH to an acid side in the
stripping process after metal ions are extracted in an alkaline
region. Therefore, by allowing of the acidic extractant that has
extracted the lithium ions in an alkaline region by addition of the
alkali solution to be in contact with a solution adjusted to
acidity, the lithium ions are stripped in the solution with a
higher concentration than the concentration of the first extracted
lithium-containing solution (about several g/l).
[0081] To be specific, in the stripping process, by allowing of the
acidic extractant extracted in the extraction process to be in
contact with the acid solution having pH 3 or less, ion exchange
between the lithium ions and H.sup.+ is caused and the lithium ions
are taken in to the solution.
[0082] As the acid solution used in the stripping process, a
sulfuric acid solution, a hydrochloric acid solution, or the like
can be used. pH of the acid solution is adjusted to 3 or less, and
is caused to be in contact with the acidic extractant that has
extracted the lithium ions in the extraction process.
[0083] Further, in the stripping process, lithium
hexafluorophosphate that has not been hydrolyzed in the precipitate
formation treatment and has been extracted in the extraction
process with the lithium ions is decomposed, and a larger amount of
lithium ions is stripped and can be taken in to the solution. That
is, in the extraction process, the lithium ions are extracted by
performing of the extraction treatment by using the acidic
extractant. At this time, lithium hexafluorophosphate that has not
been hydrolyzed and remained in the solution is extracted in the
extractant together with the lithium ions due to influence of
entrainment, and the like. Therefore, in the stripping process, by
cleaning of the extractant with an acid solution, the extracted
lithium hexafluorophosphate is separated into Li.sup.+ and
PF.sub.6.sup.-, and only the lithium ions can be stripped.
[0084] As described above, in the lithium recovery process, the
lithium ions are extracted from the solution, such as the discharge
liquid and the cleaning liquid containing lithium by using the
solvent extraction method, for example, and the extracted lithium
ions can be taken in to the solution.
[0085] Note that, in the solvent extraction method, a scrubbing
process is provided after the extraction process with the acidic
extractant, impurities extracted by the acidic extractant are
removed with the acidic extractant, and the stripping process may
then be performed. In the scrubbing process, known scrubbing
treatment, such as allowing a dilute acid to be in contact with the
solution, is performed. Accordingly, the impurities, such as iron,
which has been extracted in the acidic extractant together with the
lithium ions, can be separated and removed, and lithium of higher
purity can be recovered in the stripping process.
[0086] Further, a carbon dioxide gas or a water-soluble carbonate
is added to the stripping liquid including the lithium ions
obtained by the solvent extraction method, the gas or the carbonate
and the liquid are mixed and stirred, and lithium carbonate is
deposited and lithium may be recovered. In this way, by further
adding of a carbonate dioxide gas or a water-soluble carbonate to
the extraction liquid including lithium ions as a carbonate
fixation process (lithium carbonate deposition process), the
extracted lithium can be recovered as a solid.
[0087] As the water-soluble carbonate used in the carbonate
fixation process, a sodium carbonate solution or a calcium
carbonate solution, or the like can be used. Further, the
concentration of the solution carbonate is, but not limited to, 100
to 200 g/l, for example.
[0088] In the carbonate fixation process, the temperature of the
stripping liquid containing the lithium ions is preferably 60 to
80.degree. C. The lithium carbonate that is a carbonate of lithium
has a different solubility from other salts, and when the
temperature of the solution becomes higher, the solubility is
drastically decreased. Therefore, by increasing of the temperature
of a high-concentration lithium ion solution to 60.degree. C. or
more, the solubility of the lithium carbonate becomes lower than
other salts, such as sodium sulfate having high solubility, and
thus the lithium carbonate can be selectively precipitated as a
crystal, and a lithium carbonate solid of high purity can be
obtained. Note that it is better that the temperature of the
high-concentration lithium ion solution be higher. However, when
the temperature becomes higher than 80.degree. C., typically, an
operation becomes difficult from the viewpoint of heat resistance
of a reaction vessel or peripheral devices, and the cost is
increased. Therefore, the temperature is preferably set to 60 to
80.degree. C.
[0089] Carbonation Method
[0090] Meanwhile, when the concentration of the lithium ions in the
solution is high, for example, when lithium exceeding 1 g/l is
contained in the solution, lithium can be recovered by performing
of carbonation treatment to filtrate, from which the precipitate
formed in the precipitate formation treatment has been separated
and removed.
[0091] Examples of a carbonation agent used in the carbonation
include water-soluble carbonates, such as a sodium carbonate
solution and a potassium carbonate solution, and these
water-soluble carbonates can be preferably used from the viewpoint
of economic performance and availability. Especially, the potassium
carbonate solution can be more preferably used in terms of high
solubility and capability of decreasing the solubility of the
crystal of the formed lithium carbonate.
[0092] Further, an additive amount of the carbonation agent added
to the filtrate is not limited, and the solubility of the lithium
carbonate can be decreased by common ion effect by excessive
addition of an equivalent or more.
[0093] As described above, in the lithium recovery process, lithium
in the filtrate can be efficiently recovered by using of the
solvent extraction method or the carbonation method. Especially, in
the present embodiment, the hexafluorophosphate ions are hydrolyzed
and a precipitate of phosphorus and fluorine is formed as the
precipitate formation treatment prior to the lithium recover
process, and lithium is recovered from a filtrate from which the
phosphorus and fluorine have been separated and removed. Therefore,
the impurities of phosphorus and fluorine are not mixed in the
recovered lithium, and lithium of high purity without
contaminations can be efficiently recovered.
[0094] Note that phosphorus and fluorine have been effectively
removed from the lithium recovered as a lithium carbonate, and the
like. Therefore, by performing of double decomposition treatment,
concentration, and crystallization with calcium hydroxide, and the
like according to the rule, lithium hydroxide for lithium ion
secondary battery can be easily generated.
3. Other Embodiments
[0095] The present invention is not limited to the above-described
embodiments, and can be appropriately changed within a scope not to
change the gist of the present invention.
[0096] To be specific, processes of recovering valuable metals from
a lithium ion battery is not limited to the above processes, and
may include other processes.
[0097] Further, as the lithium-containing solution, filtrate
discharged from the positive electrode active material exfoliation
process is used, other than the above-described process liquids or
filtrate of post-sulfidation process, and alkali hydroxide is added
to the filtrate and the filtrate is made to have pH 9 or more, a
precipitate of a phosphate and a fluoride salt is formed, and
lithium may be recovered. That is, in the positive electrode active
material exfoliation process, while solid portions, such as a
positive electrode active material and an aluminum foil, are
separated, process liquids, such as an acid solution used in the
exfoliation treatment and a surfactant solution, other than the
solid portions, are discharged as the filtrate. In the filtrate,
the electrolyte and the electrolyte solution that have not been
removed in the cleaning process may sometimes be contained, and
lithium is recovered. Therefore, this filtrate can be used as an
object from which lithium is recovered.
EXAMPLES
4. Examples
[0098] Hereinafter, the present invention will be described using
examples. However, the present invention is not limited to the
examples.
(A Process of Recovering Valuable Metals from a Lithium Ion
Battery)
[0099] First, to avoid danger of combustion, and the like, in the
treatment, a used lithium ion battery was immersed in a sodium
chloride solution of 100 g/L, which is a discharge liquid, and was
made to be in a discharge state. Note that an end point of
discharge was determined by absence of hydrogen by using a hydrogen
gas sensor. After the discharge treatment, slurry was filtered, and
a discharged discharge liquid was recovered. Then, the discharged
lithium ion battery was dismantled into a size of 1 cm square or
less by a biaxial crusher, and dismantled objects of the battery
were obtained.
[0100] Next, the obtained dismantled objects of the battery were
cleaned with water, and an electrolyte solution and an electrolyte
contained in the dismantled objects of the battery were removed.
After the cleaning treatment, the slurry was filtered, and the
cleaning liquid (water) containing an electrolyte solution and an
electrolyte was recovered.
[0101] Meanwhile, water containing 1.8 weight % of polyoxyethylene
octylphenylether (the product name: EMULGEN series manufactured by
Kao Corporation), which is surfactant, was added to solid portions
separated with a screen from the dismantled objects of the battery
of post-cleaning treatment. An exfoliation operation by stirring
was performed, and a positive electrode active material was
recovered.
[0102] The exfoliated positive electrode active material was
leached with a sulfuric acid (H.sub.2SO.sub.4) solution of the
concentration of 200 g/l, and nickel and cobalt that are valuable
metals were leached. Next, as a sulfidation process, an obtained
leachate was used, and sodium sulfide (Na.sub.2S) was added to the
leachate as a sulfidation agent, and nickel/cobalt mixture sulfide
was obtained. After a precipitate of the nickel/cobalt mixture
sulfide was separated, obtained filtrate was recovered.
A Lithium Recovery Operation from a Discharge Liquid and a Cleaning
Liquid
Example 1
[0103] In the above-described operation of recovering valuable
metals from a used lithium ion battery, by filtering of the slurry
recovered after the discharge treatment and the cleaning treatment,
and the slurry of post-sulfidation process, the process liquid made
of the discharge liquid and the cleaning liquid of post-treatment
and the filtrate of post-sulfidation process were obtained. Table 1
shows composition of the obtained solution.
TABLE-US-00001 TABLE 1 Li P F Composition of lithium-containing
solution (g/l) 5.3 0.4 1.3
[0104] As shown in Table 1, the solution contained lithium based on
lithium hexafluorophosphate of a positive electrode active
material. The following operation was continued by using the
lithium-containing solution as an object from which lithium is
recovered.
[0105] First, an 8 mol/l sodium hydroxide (NaOH) solution was added
to the lithium-containing solution of 100 ml shown in Table 1, the
solution was adjusted to have pH 9.5, and hexafluorophosphate ions
contained in the solution were hydrolyzed. Then, the solution was
stirred at room temperature until generation of a precipitate of
the hydrolyzed phosphate ions or fluoride ions and lithium is
completed. The generation of the precipitate ended after one hour,
the generated precipitate was filtered. Table 2 shows composition
of the filtrate obtained after the filtration.
TABLE-US-00002 TABLE 2 Li P F Composition of solution after alkali
decomposition 3.9 0.1 0.2 (g/l)
[0106] As shown in Table 2, little phosphorus and fluorine were
contained in the filtrate after the filtration. This can be
considered that the hexafluorophosphate ions were hydrolyzed by
increasing of pH by addition of the sodium hydroxide solution, and
the phosphate ions and the fluoride ions generated by being
hydrolyzed formed the precipitate of a phosphate and a fluoride
salt with the lithium ions in the solution. It can be considered
that, by removing of the precipitate, phosphorus and fluorine in
the solution were able to be effectively separated and removed.
[0107] Next, an extraction solvent made of a mixed liquid 100 ml of
50 v/v % D2EHPA (manufactured by LANXESS K.K.) and 50 v/v % DIBK
(manufactured by Kyowa Hakko Co., Ltd.) was added to the solution
(filtrate) shown in Table 2, and solvent extraction treatment to
extract lithium from the filtrate was performed. At that time, the
8 mol/l sodium hydroxide solution was added to the solution, the
solution was mixed, and pH was adjusted to 11. After the adjustment
of pH, an operation to add a new mixture of the extraction solvent
when the extraction solvent was separated was repeated five times,
and a solvent extraction operation was performed. With the
operation, an extraction residual liquid of 120 ml was finally
obtained. Table 3 shows composition of the obtained extraction
residual liquid.
TABLE-US-00003 TABLE 3 Li P F Composition of extraction residual
liquid after 0.3 0.08 0.16 solution extraction (g/l)
[0108] As shown in Table 3, 90.0% of lithium ions were able to be
extracted with the extraction solvent. Phosphorus and fluorine were
merely diluted 1.2 times, and precipitate or co-extraction was not
found during the operation.
[0109] Next, the extracted solvents of five times were summed up,
and after filtration, the solvent were stripped with 1 mold
hydrochloric acid of 100 ml, having pH 3. Table 4 shows composition
of the stripping liquid.
TABLE-US-00004 TABLE 4 Li P F Composition of stripping liquid after
3.6 <0.01 <0.01 solution extraction (g/l)
[0110] As shown in Table 4, the stripping liquid contained lithium
of 3.6 g/l, and lithium was able to be taken into the solution.
Further, detection values of phosphorus and fluorine were a lower
detection limit (0.01 g/l) or less, and lithium was able to be
efficiently recovered without contamination by phosphorus and
fluorine.
Example 2
[0111] In Example 2, an operation was performed by a similar method
to Example 1 except that an 8 mol/l potassium hydroxide (KOH)
solution was used as the alkali hydroxide to be added instead of
the sodium hydroxide solution in the hydrolysis treatment of the
hexafluorophosphate ions by addition of alkali hydroxide and in the
precipitate formation treatment in Example 1. Table 5 shows
analysis values of the filtrate of post-hydrolysis treatment with
the potassium hydroxide solution and a precipitate formation
treatment.
TABLE-US-00005 TABLE 5 Li P F Composition of solution after
addition of KOH 3.7 0.05 0.12 (g/l)
[0112] As shown in Table 5, when the potassium hydroxide solution
was added, the solubility of a phosphate and a fluoride salt was
able to be decreased, compared with the case where the sodium
hydroxide solution was added in Example 1, and a precipitate of the
slightly soluble salts was able to be efficiently removed.
Therefore, the content of phosphorus and fluorine in the filtrate
was able to be further decreased.
Example 3
[0113] In Example 3, after a solution made of the composition of
Table 2 was obtained by the same method as Example 1, next, a
sodium carbonate solution or a potassium carbonate solution was
added until saturated, and lithium was recovered as a crystal of
lithium carbonate by carbonation treatment. That is, different from
Example 1, filtrate after precipitate treatment was subjected to
the carbonation treatment instead of the solvent extraction
treatment, and lithium was recovered. Table 6 shows analysis values
of a mother liquor of post-carbonation treatment, and Table 7 shows
the quality of a crystal of lithium carbonate.
TABLE-US-00006 TABLE 6 Carbonation agent Li P F Composition of
mother liquor Na.sub.2CO.sub.3 0.4 0.08 0.16 after carbonation
(g/l) K.sub.2CO.sub.3 0.2 0.07 0.14
TABLE-US-00007 TABLE 7 Carbonation agent Li P F Quality of crystal
of lithium carbonate Na.sub.2CO.sub.3 -- <0.01 <0.01 (%)
K.sub.2CO.sub.3 -- <0.01 <0.01
[0114] As shown in Tables 6 and 7, in the carbonation treatment,
even when a sodium carbonate (Na.sub.2CO.sub.3) solution or a
potassium carbonate (K.sub.2CO.sub.3) solution was used as a
carbonation agent, detection values of phosphorus and fluorine
contained in the crystal of lithium carbonate were a lower
detection limit (0.01 g/l) or less, and lithium without containing
the impurities of phosphorus and fluorine was able to be recovered
as a carbonate.
[0115] As described above, by removing of phosphorus and fluorine
to a solubility level prior to the recovery of lithium by the
carbonation treatment, the solubility by addition of the
water-soluble carbonate, such as sodium carbonate or potassium
carbonate, is not decreased. Therefore, it was confirmed that the
lithium carbonate was able to be recovered without contamination of
phosphorus and fluorine.
[0116] As can be seen from the above examples, the alkali hydroxide
is added to the discharge liquid and the cleaning liquid as the
precipitate formation treatment, prior to the recovery of lithium
of the solvent extraction treatment and the carbonation treatment
and pH is raised, slightly soluble salts of a phosphate and a
fluoride salt are formed, and phosphorus and fluorine are removed,
whereby lithium can be recovered without contamination by
phosphorus and fluorine.
Comparative Example 1
[0117] Meanwhile, in Comparative Example 1, a solvent extraction
operation was directly performed to a solution shown in Table 1
recovered from a discharge liquid and a cleaning liquid without
performing hydrolysis treatment by addition of alkali hydroxide and
precipitate formation treatment like the above examples.
[0118] As a result, at a timing when pH was raised to 9 in a
solvent extraction process, a large volume of a precipitate of a
phosphate and a fluoride salt was generated and phase separation
became difficult, and a large volume of the precipitate was mixed
in to an organic phase from which lithium was extracted.
Comparative Example 2
[0119] Further, in Comparative Example 2, carbonation treatment was
performed to a solution shown in Table 1 recovered from a discharge
liquid and a cleaning liquid without performing hydrolysis
treatment by addition of alkali hydroxide and precipitate formation
treatment like the above examples.
[0120] As a result, in the vicinity of pH 9 where carbonation is
started, a precipitate of a phosphate and a fluoride salt was
generated, and the solution became muddy. Table 8 shows the quality
of the generated carbonate precipitate.
TABLE-US-00008 TABLE 8 Carbonation agent Li P F Quality of crystal
of lithium carbonate (%) Na.sub.2CO.sub.3 -- 1.9 8.9
K.sub.2CO.sub.3 -- 2.0 9.2
[0121] As shown in Table 8, even when a sodium carbonate
(Na.sub.2CO.sub.3) solution or a potassium carbonate
(K.sub.2CO.sub.3) solution was used as a carbonation agent, the
generated carbonate contains a large volume of phosphorus and
fluorine, and only contaminated lithium can be recovered and did
not satisfy the quality that can be used as a lithium compound for
manufacturing a positive electrode active material again.
* * * * *